Paris Classification of inflammatory bowel disease

Last revised by Hao Ting (Jacky) Liao on 9 Jan 2023

The Paris Classification of inflammatory bowel disease is used to classify the severity of ulcerative colitis and Crohn disease in the pediatric population. Primary differences between the adult and pediatric phenotype include the location, behavior, propensity for disease extension as well as its effect on growth 1.  

As with the Montreal Classification, the Paris classification acts as a guide for clinical management as well as discern the risk of future complications. It is used in conjunction with the Montreal classification as opposed to replacing it 1.

There are four categories in relation to Crohn disease, Age of onset and location provide descriptions in the nature of disease and can assist with determination of risk for progression and complications. Behavior and growth provide an insight into the severity of disease, with increase in sub-categories reflect severity.

This is also the case for ulcerative colitis. Severity of disease now utilizes the pediatric ulcerative colitis activity index (PUCAI) point system; where >65 points would indicate severe disease and would therefore reflect as S1 in the classification 2.

  • age

    • A1a: 0 to <10 years

    • A1b: 10 to <17 years

    • A2: 17-40 years

    • A3: > 40 years

  • location

    • L1: distal 1/3 ileal +/- limited cecal disease

    • L2: colonic

    • L3: ileocolonic

    • L4a: upper disease proximal to Ligament of Treitz

    • L4b: upper disease distal to Ligament of Treitz and proximal to distal 1/3 ileum

  • behavior

    • B1: non-stricturing Non-penetrating

    • B2: stricturing

    • B3: penetrating

    • B2B3: both  penetrating and structuring disease either at the same or different times

    • P: peri-anal disease modifier

  • growth

    • G0: no evidence of growth delay

    • G1: growth delay

  • extent of disease

    • E1: ulcerative proctitis

    • E2: left-sided ulcerative colitis – distal to splenic-flexure

    • E3: extensive disease – distal to hepatic flexure

    • E4: pan-colitis – proximal to hepatic flexure

  • severity

    • S0: never severe

    • S1: severe 

The Paris classification is built upon the Montreal classification to better capture the dynamic nature and complexities of the pediatric disease phenotype; the Montreal Classification has shown to have moderate inter-rate reliability when used in pediatric populations 1,3. This is among the list of revisions to the international classification system for inflammatory bowel disease, including Rome in 1991, Vienna in 1998 and Montreal in 2005.

The revisions made from the Montreal classification with relation to Crohn disease include better categorization of age, disease location and behavior for the pediatric phenotype. As pediatric Crohn disease tends to be more aggressive than the adult phenotype and involve more of the proximal colon, more detailed classification of severity regarding colon involvement was required 2,3. Furthermore, a new category of growth impairment was added as it is a significant element of Crohn disease in pediatric population 4.

With regard to ulcerative colitis, disease location and severity are better defined in the Paris classification, with further sub-categorization within the disease location to fit the pediatric phenotype 1,5.

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